Amine-aldehyde resins and uses thereof in separation processes

ABSTRACT

Amine-aldehyde resins are disclosed for removing a wide variety of solids and/or ionic species from the liquids in which they are suspended and/or dissolved. These resins are especially useful as froth flotation depressants in the separation of bitumen from sand and/or clay or in the beneficiation of clay (e.g., kaolin clay) from an impure clay-containing ore. The resins are also useful for treating aqueous liquid suspensions to remove solid particulates, as well as for removing metallic ions in the purification of water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalPatent Application No. 60/683,143, filed Dec. 23, 2004, and 60/713,340,filed Sep. 2, 2005, each of which is hereby incorporated by reference inits entirety.

FIELD OF THE INVENTION

The present invention relates to resins for use in separation processes,and especially the selective separation of solids and/or ionic speciessuch as metallic cations from aqueous media. Such processes includefroth flotation (e.g., used in the purification of clay-containingores), the separation of drill cuttings from oil drilling fluids, clayand coal slurry dewatering, sewage treatment, pulp and paper milleffluent processing, the removal of sand from bitumen, and thepurification of water to render it potable. The resins comprise thereaction product of a primary or secondary amine and an aldehyde (e.g.,a urea-formaldehyde resin).

BACKGROUND OF THE INVENTION

Froth Flotation

Industrially, processes for the purification of liquid suspensions ordispersions (and especially aqueous suspensions or dispersions) toremove suspended solid particles are quite prevalent. Froth flotation,for example, is a separation process based on differences in thetendency of various materials to associate with rising air bubbles.Additives are often incorporated into the froth flotation liquid (e.g.,aqueous brine) to improve the selectivity of the process. For example,“collectors” can be used to chemically and/or physically absorb ontomineral(s) to be floated, rendering them more hydrophobic. On the otherhand, “depressants,” typically used in conjunction with collectors,render other materials (e.g., gangue minerals) less likely to associatewith the air bubbles, and therefore less likely to be carried into thefroth concentrate.

In this manner, some materials (e.g., value minerals) will, relative toothers (e.g., gangue materials), exhibit preferential affinity for airbubbles, causing them to rise to the surface of the aqueous slurry,where they can be collected in a froth concentrate. A degree ofseparation is thereby effected. In less common, so-called reverse frothflotations, it is the gangue that is preferentially floated andconcentrated at the surface, with the desired materials removed in thebottoms. Gangue materials typically refer to quartz, sand and claysilicates, and calcite, although other minerals (e.g., fluorite, barite,etc.,) may be included. In some cases, the material to be purified(i.e., the desired material) actually comprises predominantly suchmaterials, and the smaller amounts of contaminants are preferentiallyfloated. For example, in the beneficiation of kaolin clay, a materialhaving a number of industrially significant applications, iron andtitanium oxides can be separated by flotation from the impure,clay-containing ore, leaving a purified kaolin clay bottoms product.

The manner in which known collectors and depressants achieve theireffect is not understood with complete certainty, and several theorieshave been proposed to date. Depressants, for example may prevent thegangue minerals from adhering to the value materials to be separated, orthey may even prevent the collector(s) from absorbing onto the gangueminerals. Whatever the mechanism, the ability of a depressant to improvethe selectivity in a froth flotation process can very favorably impactits economics.

Overall, froth flotation is practiced in the beneficiation of a widevariety of value materials (e.g., mineral and metal ores and even highmolecular weight hydrocarbons such as bitumen), in order to separatethem from unwanted contaminants which are unavoidably co-extracted fromnatural deposits. A particular froth flotation process of commercialsignificance involves the separation of bitumen from sand and/or clay,which are ubiquitous in oil sand deposits, such as those found in thevast Athabasca region of Alberta, Canada. Bitumen is recognized as avaluable source of “semi-solid” petroleum or heavyhydrocarbon-containing crude oil, which can be upgraded into manyvaluable end products including transportation fuels such as gasoline oreven petrochemicals. Alberta's oil sand deposits are estimated tocontain 1.7 trillion barrels of bitumen-containing crude oil, exceedingthe reserves in all of Saudi Arabia. For this reason, significant efforthas been recently expended in developing economically feasibleoperations for bitumen recovery, predominantly based on subjecting anaqueous slurry of extracted oil sand to froth flotation. For example,the “Clark Process” involves recovering the bitumen in a frothconcentrate while depressing the sand and other solid impurities.

Various gangue depressants for improving froth flotation separations areknown in the art and include sodium silicate, starch, tannins, dextrins,lignosulphonic acids, carboxylmethyl cellulose, cyanide salts and manyothers. More recently certain synthetic polymers have been foundadvantageous in particular beneficiation processes. For example, U.S.Pat. No. Re. 32,875 describes the separation of gangue from phosphateminerals (e.g., apatite) using as a depressant a phenol-formaldehydecopolymer (e.g., a resol, a novolak) or a modified phenol polymer (e.g.,a melamine-modified novolak).

U.S. Pat. No. 3,990,965 describes the separation of iron oxide frombauxite using as a depressant a water soluble prepolymer of low chainlength that adheres selectively to gangue and that can be furtherpolymerized to obtain a cross-linked, insoluble resin.

U.S. Pat. No. 4,078,993 describes the separation of sulfide or oxidizedsulfide ores (e.g., pyrite, pyrrhotite, or sphalerite) from metalmineral ores (e.g., copper, zinc, lead, nickel) using as a depressant asolution or dispersion of a low molecular weight condensation product ofan aldehyde with a compound containing 2-6 amine or amide groups.

U.S. Pat. Nos. 4,128,475 and 4,208,487 describe the separation of ganguematerials from mineral ore using a conventional frothing agent (e.g.,pine oils) combined with a (preferably alkylated) amino-aldehyde resinthat may have free methylol groups.

U.S. Pat. No. 4,139,455 describes the separation of sulfide or oxidizedsulfide ores (e.g., pyrite, pyrrhotite, or sphalerite) from metalmineral ores (e.g., copper, zinc, lead, nickel) using as a depressant anamine compound (e.g., a polyamine) in which at least 20% of the totalnumber of amine groups are tertiary amine groups and in which the numberof quaternary amine groups is from 0 to not more than ⅓ the number oftertiary amine groups.

U.S. Pat. No. 5,047,144 describes the separation of siliceous materials(e.g., feldspar) from minerals (e.g., kaolinite) using as a depressant acation-active condensation product of aminoplast formers withformaldehyde, in combination with cation-active tensides (e.g., organicalkylamines) or anion-active tensides (e.g, long-chained alkylsulfonates).

Russian Patent Nos. 427,737 and 276,845 describe the depression of clayslime using carboxymethyl cellulose and urea-formaldehyde resins,optionally combined with methacrylic acid-methacrylamide copolymers orstarch ('845 patent).

Russian Patent Nos. 2,169,740; 2,165,798; and 724,203 describe thedepression of clay carbonate slimes from ores in the potassium industry,including sylvinite (KCl—NaCl) ores. The depressant used is aurea/formaldehyde condensation product that is modified bypolyethylenepolyamine. Otherwise, a guanidine-formaldehyde resin isemployed ('203 patent).

Markin, A. D., et. al., describe the use of urea-formaldehyde resins ascarbonate clay depressors in the flotation of potassium ores. Study ofthe Hydrophilizing Action of Urea-Formaldehyde Resins on Carbonate ClayImpurities in Potassium Ores, Inst. Obshch. Neorg. Khim, USSR, VestsiAkademii Navuk BSSR, Seryya Khimichnykh Navuk (1980); Effect ofUrea-Formaldehyde Resins on the Flotation of Potassium Ores,Khimicheskaya Promyshlennost, Moscow, Russian Federation (1980); andAdsorption of Urea-Formaldehyde Resins on Clay Minerals of potassiumOres, Inst. Obshch Neorg. Khim., Minsk, USSR, Doklady Akademii Nauk BSSR(1974).

As is recognized in the art, a great diversity of materials can besubject to beneficiation/refinement by froth flotation. Likewise, thenature of both the desired and the unwanted components varies greatly.This is due of the differences in chemical composition of thesematerials, as well as in the types of prior chemical treatment andprocessing steps used. Consequently, the number and type of frothflotation depressants is correspondingly wide.

Also, the use of a given depressant in one service (e.g., raw potassiumore beneficiation) is not a predictor of its utility in an applicationinvolving a significantly different feedstock (e.g., bitumen-containingoil sand). This also applies to any expectation regarding the use of adepressant that is effective in froth flotation, in the any of theseparations of solid contaminants from aqueous liquid suspensions,described below (and vice versa). The theoretical mechanisms by whichfroth flotation and aqueous liquid/solid separations occur aresignificantly different, where the former process relies on differencesin hydrophobicity and the latter on several other possibilities (chargedestabilization/neutralization, agglomeration, host-guest theory(including podands), hard-soft acid base theory, dipole-dipoleinteractions, Highest Occupied Molecular Orbital-Lowest unoccupiedMolecular Orbital (HOMO-LUMO) interactions, hydrogen bonding, Gibbs freeenergy of bonding, etc). Traditional depressants in froth flotation forthe benefication of metallic ores, such as guar gum, are not employed asdewatering agents, or even as depressants in froth flotation for bitumenseparation. Moreover, in two of the applications described below (wasteclay and coal dewatering), no agents are currently used to improve thesolid/liquid separation. Overall, despite the large offering offlotation depressants and dewatering agents in the art, an adequatedegree of refinement in many cases remains difficult to achieve. Thereis therefore a need in the art for agents which can be effectivelyemployed in a wide range of separation processes, including both frothflotation and the separation of solid contaminants from liquidsuspensions.

Other Separations

Other processes, in addition to froth flotation, for the separation ofsolid contaminants from liquid suspensions can involve the use ofadditives that either destabilize these suspensions or otherwise bindthe contaminants into larger agglomerates. Coagulation, for example,refers to the destabilization of suspended solid particles byneutralizing the electric charge that separates them. Flocculationrefers to the bridging or agglomeration of solid particles together intoclumps or flocs, thereby facilitating their separation by settling orflotation, depending on the density of the flocs relative to the liquid.Otherwise, filtration may be employed as a means to separate the largerflocs.

The additives described above, and especially flocculants, are oftenemployed, for example, in the separation of solid particles of rock ordrill cuttings from oil and gas well drilling fluids. These drillingfluids (often referred to as “drilling muds”) are important in thedrilling process for several reasons, including cooling and lubricatingthe drill bit, establishing a fluid counterpressure to preventhigh-pressure oil, gas, and/or water formation fluids from entering thewell prematurely, and hindering the collapse of the uncased wellbore.Drilling muds, whether water- or oil-based, also remove drill cuttingsfrom the drilling area and transport them to the surface. Flocculantssuch as acrylic polymers are commonly used to agglomerate these cuttingsat the surface of the circulating drilling mud, where they can beseparated from the drilling mud.

Other uses for flocculants in solid/liquid separations include theagglomeration of clays which are suspended in the large waste slurryeffluents from phosphate production facilities. Flocculants such asanionic natural or synthetic polymers, which may be combined with afibrous material such as recycled newspaper, are often used for thispurpose. The aqueous clay slurries formed in phosphate purificationplants typically have a flow rate of over 100,000 gallons per minute andgenerally contain less than 5% solids by weight. The dewatering (e.g.,by settling or filtration) of this waste clay, which allows for recycleof the water, presents one of the most difficult problems associatedwith reclamation. The settling ponds used for this dewatering normallymake up about half of the mined area, and dewatering time can be on theorder of several months to several years.

In the separation of solids from aqueous liquids, other specificapplications of industrial importance include the filtration of coalfrom water-containing slurries (i.e., slurry dewatering), the treatmentof sewage to remove contaminants (e.g., sludge) via sedimentation, andthe processing of pulp and paper mill effluents to remove suspendedcellulosic solids. The dewatering of coal poses a significant problemindustrially, as the BTU value of coal decreases with increasing watercontent. Raw sewage, both industrial and municipal, requires enormoustreatment capacity, as wastes generated by the U.S. population, forexample, are collected into sewer systems and carried along byapproximately 14 billion gallons of water per day. Paper industryeffluent streams likewise represent large volumes of solid-containingaqueous liquids, as waste water generated from a typical paper plantoften exceeds 25 million gallons per day. The removal of sand fromaqueous bitumen-containing slurries generated in the extraction andsubsequent processing of oil sands, as described previously, posesanother commercially significant challenge in the purification ofaqueous liquid suspensions. Also, the removal of suspended solidparticulates is often an important consideration in the purification ofwater, such as in the preparation of drinking (i.e., potable) water.Synthetic polyacrylamides, as well as naturally-occurring hydrocolloidalpolysaccharides such as alginates (copolymers of D-mannuronic andL-guluronic acids) and guar gum are flocculants in this service.

The above applications therefore provide several specific examplesrelating to the treatment of aqueous liquid suspensions to remove solidparticulates. However, such separations are common in a vast number ofother processes in the mineral, chemical, industrial and municipalwaste, sewage treatment, and paper industries, as well as in a widevariety of other water-consuming industries. Thus, there is a need inthe art for additives that can effectively promote selective separationof a variety of solid contaminants from liquid suspensions.Advantageously, such agents should be selective in chemicallyinteracting with the solid contaminants, through coagulation,flocculation, or other mechanisms such that the removal of thesecontaminants is easily effected. Especially desirable are additives thatare also able to complex unwanted ionic species such as metal cations tofacilitate their removal as well.

SUMMARY OF THE INVENTION

All Uses

The present invention is directed to amine-aldehyde resins for removing,generally in a selective fashion, a variety of solids and/or ionicspecies from the liquids in which they are suspended and/or dissolved.These resins are highly versatile, as they are especially useful asfroth flotation depressants in the separation of bitumen from sandand/or clay or in the purification of clay (e.g., kaolin clay) from aclay-containing ore. The amine-aldehyde resins are also useful fortreating aqueous liquid suspensions (e.g., aqueous suspensionscontaining sand, clay, coal, and/or other solids, such as used drillcutting fluids, as well as process and effluent streams in phosphate andcoal production, sewage treatment, paper manufacturing, or bitumenrecovery facilities) to remove solid particulates and also potentiallymetallic cations (e.g., in the purification of drinking water).

Froth Flotation

Without being bound by theory, the amine-aldehyde resins of the presentinvention are highly selective in froth flotation processes for (1)binding to sand and/or clay to purify bitumen, as well as (2) refiningclay-containing ores. Also, because these resins have affinity forwater, the sand and/or clay particles, which interact and associate withthe resin, are effectively sequestered in the aqueous phase in frothflotation. Consequently, sand and/or clay can be selectively separatedfrom bitumen or impurities in clay-containing ores such as iron oxide.

Accordingly, in one embodiment, the present invention is a method forpurifying bitumen from a bitumen-containing slurry comprising sand orclay. The method comprises treating the slurry with a depressantcomprising a resin that is the reaction product of a primary or asecondary amine and an aldehyde and recovering, by froth flotationeither after or during the treating step, purified bitumen having areduced amount of sand or clay. In another embodiment, the resin is aurea-formaldehyde resin, which is typically the reaction product of ureaand formaldehyde at a formaldehyde:urea (F:U) molar ratio from about1.75:1 to about 3:1. In another embodiment, the depressant comprises aresin in a solution or dispersion having a resin solids content fromabout 30% to about 90% by weight.

In another embodiment, the present invention is a method for purifyingclay from a clay-containing ore comprising an impurity selected from ametal, a metal oxide, a mineral, and mixtures thereof. The methodcomprises treating a slurry of the clay-containing ore with a depressantcomprising a resin and recovering, by froth flotation of the impurityeither after or during the treating step, a purified clay having areduced amount at least one of the impurities. The resin is the reactionproduct of a primary or a secondary amine and an aldehyde. In anotherembodiment, the clay-containing ore comprises kaolin clay. In anotherembodiment, the impurity comprises a mixture of iron oxide and titaniumdioxide. In another embodiment, the impurity comprises coal.

Other Separations

In another embodiment, the present invention is a method for purifyingan aqueous liquid suspension comprising a solid contaminant. The methodcomprises treating the liquid suspension with a resin as described aboveand removing, either after or during the treating step, (1) at least aportion of the solid contaminant in a contaminant-rich fraction and/or(2) a purified liquid. In another embodiment, the treating stepcomprises flocculating the solid contaminant (e.g., sand or clay). Inanother embodiment, the removing step is carried out by sedimentation,flotation, or filtration. In another embodiment, the liquid suspensionis an oil well drilling fluid and the method comprises removing apurified drilling fluid for reuse in oil well drilling. In anotherembodiment, the aqueous liquid suspension is a clay-containing effluentslurry from a phosphate production facility and the method comprisesremoving purified water for reuse in phosphate production. In anotherembodiment, the aqueous liquid suspension is an aqueous coal-containingsuspension and the method comprises removing a coal-rich fraction byfiltration. In another embodiment, the aqueous liquid suspensioncomprises sewage and the method comprises removing purified water bysedimentation. In another embodiment, the aqueous liquid suspensioncomprises a pulp or paper mill effluent, the solid contaminant comprisesa cellulosic material, and the method comprises removing purified water.In another embodiment, the aqueous liquid suspension is a bitumenproduction process intermediate or effluent slurry comprising sand orclay. In still another embodiment, the purified liquid is potable water.

In another embodiment, the present invention is a method for purifyingwater comprising a metallic cation. The method comprises treating thewater with the resin described above and removing at least a portion ofthe metallic cation by filtration to yield purified water (e.g., potablewater). In another embodiment, the removing step comprises membranefiltration. In another embodiment, the metallic cation is selected fromthe group consisting of As⁺⁵, Pb⁺², Cd⁺², Cu⁺², Mn⁺², Hg⁺², and mixturesthereof. In yet another embodiment, the resin is modified with ananionic functional group.

These and other embodiments are apparent from the following DetailedDescription.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a photograph of four jars containing graphite (two left jars)and bentonite (two right jars) that were left to stand for 24 hoursafter vigorous shaking to suspend these solids in water. The leftmostjar and the third jar from the left were treated with Urea-Formaldehyderesin prior to shaking.

DETAILED DESCRIPTION OF THE INVENTION

All Uses

The resin that is used in separation processes of the present inventionis the reaction product of a primary or secondary amine and an aldehyde.The primary or secondary amine, by virtue of having a nitrogen atom thatis not completely substituted (i.e., that is not part of a tertiary orquaternary amine) is capable of reacting with an aldehyde, to form anadduct. If formaldehyde is used as the aldehyde, for example, the adductis a methylolated adduct having reactive methylol functionalities.Typical primary and secondary amines used to form the resin includecompounds having at least two functional amine or amide groups, oramidine compounds having at least one of each of these groups. Suchcompounds include ureas, guanidines, and melamines, which may besubstituted at their respective amine nitrogen atoms with aliphatic oraromatic radicals, wherein at least two nitrogen atoms are notcompletely substituted. Often, the primary amines are used. Urea isrepresentative of these, due to its low cost and extensive commercialavailability. In the case of urea, if desired, at least a portionthereof can be replaced with ammonia, primary alkylamines,alkanolamines, polyamines (e.g., alkyl primary diamines such as ethylenediamine and alkyl primary triamines such as diethylene triamine),polyalkanolamines, melamine or other amine-substituted triazines,dicyandiamide, substituted or cyclic ureas (e.g., ethylene urea),primary amines, secondary amines and alkylamines, tertiary amines andalkylamines, guanidine, and guanidine derivatives (e.g., cyanoguanidineand acetoguanidine). Aluminum sulfate, cyclic phosphates and cyclicphosphate esters, formic acid or other organic acids may also be used inconjunction with urea. The amount of any one of these components (or ifused in combination then their combined amount), if incorporated intothe resin to replace part of the urea, typically will vary from about0.05 to about 20% by weight of the resin solids. These types of agentspromote hydrolysis resistance, flexibility, reduced aldehyde emissionsand other characteristics, as is appreciated by those having skill inthe art.

The aldehyde used to react with the primary or secondary amine asdescribed above, to form the resin, may be formaldehyde, or otheraliphatic aldehydes such as acetaldehyde and propionaldehyde. Aldehydesalso include aromatic aldehydes (e.g., benzylaldehyde and furfural), andother aldehydes such as aldol, glyoxal, and crotonaldehyde. Mixtures ofaldehydes may also be used. Generally, due to its commercialavailability and relatively low cost, formaldehyde is used.

In forming the resin, the initial formation of an adduct between theamine and the aldehyde is well known in the art. The rate of thealdehyde addition reaction is generally highly dependent on pH and thedegree of substitution achieved. For example, the rate of addition offormaldehyde to urea to form successively one, two, and three methylolgroups has been estimated to be in the ratio of 9:3:1, whiletetramethylolurea is normally not produced in a significant quantity.The adduct formation reaction typically proceeds at a favorable rateunder alkaline conditions and thus in the presence of a suitablealkaline catalyst (e.g., ammonia, alkali metal hydroxides, or alkalineearth metal hydroxides). Sodium hydroxide is most widely used.

At sufficiently high pH values, it is possible for the adduct formationreaction to proceed essentially in the absence of condensation reactionsthat increase the resin molecular weight by polymerization (i.e., thatadvance the resin). However, for the formation of low molecular weightcondensate resins from the further reaction of the amine-aldehydeadduct, the reaction mixture is generally maintained at a pH typicallyfrom about 5 to about 9. If desired, an acid such as acetic acid can beadded to help control the pH and therefore the rate of condensation andultimately the molecular weight of the condensed resin. The reactiontemperature is normally in the range from about 30° C. to about 120° C.,typically less than about 85° C., and often the reflux temperature isused. A reaction time from about from about 15 minutes to about 3 hours,and typically from about 30 minutes to about 2 hours, is used inpreparing the low molecular weight amine-aldehyde condensate resin fromthe primary or secondary amine and aldehyde starting materials. Variousadditives may be incorporated, prior to or during the condensationreaction, in order to impart desired properties into the amine-aldehyderesin. For example, guar gum; carboxymethylcellulose or otherpolysaccharides such as alginates; or polyols such as polyvinylalcohols, pentaerythitol, or Jeffol™ polyols (Hunstman Corporation, SaltLake City, Utah, USA) may be used to alter the viscosity and consistencyof the final amine-aldehyde resin and improve its performance in frothflotation and other applications. Otherwise, quaternary ammonium saltsincluding diallyl dimethyl ammonium chloride (or analogs such as diallyldiethyl ammonium chloride) or alkylating agents includingepichlorohydrin (or analogs such as epibromohydrin) may be used toincrease the cationic charge of the amine-aldehyde resin and therebyimprove its performance in certain solid/liquid separations (e.g., claydewatering) discussed below. In this manner, such additives may be moreeffectively reacted into the amine-aldehyde resin than merely blendedwith the resin after its preparation.

Condensation reaction products of the amine-aldehyde, amide-aldehyde,and/or amidine-aldehyde adducts described above include, for examplethose products resulting from the formation of (i) methylene bridgesbetween amido nitrogens by the reaction of alkylol and amino groups,(ii) methylene ether linkages by the reaction of two alkylol groups,(iii) methylene linkages from methylene ether linkages with thesubsequent removal of formaldehyde, and (iv) methylene linkages fromalkylol groups with the subsequent removal of water and formaldehyde.

Generally, in preparing the resin, the molar ratio of aldehyde:primaryor secondary amine is from about 1.5:1 to about 4:1, which refers to theratio of moles of all aldehydes to moles of all amines, amides, andamidines reacted to prepare the resin during the course of the adductformation and condensation reactions described above, whether performedseparately or simultaneously. The resin is normally prepared underambient pressure. The viscosity of the reaction mixture is often used asa convenient proxy for the resin molecular weight. Therefore thecondensation reaction can be stopped when a desired viscosity isachieved after a sufficiently long time and at a sufficiently hightemperature. At this point, the reaction mixture can be cooled andneutralized. Water may be removed by vacuum distillation to give a resinwith a desired solids content. Any of a wide variety of conventionalprocedures used for reacting primary and secondary amine and aldehydecomponents can be used, such as staged monomer addition, staged catalystaddition, pH control, amine modification, etc., and the presentinvention is not limited to any particular procedure.

A representative amine-aldehyde resin for use in separation processes ofthe present invention is a urea-formaldehyde resin. As described above,a portion of the urea may be replaced by other reactive amine and/oramides and a portion of the formaldehyde may be replaced by otheraldehydes, to provide various desirable properties, without departingfrom the characterization of the resin as a urea-formaldehyde resin.Urea-formaldehyde resins can be prepared from urea and formaldehydemonomers or from precondensates in manners well known to those skilledin the art. Typically, the urea and formaldehyde are reacted at a molarratio of formaldehyde to urea (F:U) in the range from about 1.75:1 toabout 3:1, and usually at a formaldehyde:urea (F:U) mole ratio fromabout 2:1 to about 3:1, in order to provide sufficient methylolatedspecies for resin cross-linking (e.g., di- and tri-methylolated ureas).Generally, the urea-formaldehyde resin is a highly water dilutabledispersion, if not an aqueous solution.

In one embodiment, the condensation is allowed to proceed to an extentsuch that the urea-formaldehyde resin has a number average molecularweight (M_(n)), of greater than about 300 grams/mole, and often fromabout 400 to about 1200 grams/mole. As is known in the art, the value ofM_(n) of a polymer sample having a distribution of molecular weights isdefined as

${M_{n} = \frac{\sum\limits_{i}{N_{i}M_{i}}}{\sum\limits_{i}N_{i}}},$

where N_(i) is the number of polymer species having i repeat units andM_(i) is the molecular weight of the polymer species having i repeatunits. The number average molecular weight is typically determined usinggel permeation chromatography (GPC), using solvent, standards, andprocedures well known to those skilled in the art.

A cyclic urea-formaldehyde resin may also be employed and prepared, forexample, according to procedures described in U.S. Pat. No. 6,114,491.Urea, formaldehyde, and ammonia reactants are used in a mole ratio ofurea:formaldehyde:ammonia that may be about 0.1 to 1.0:about 0.1 to3.0:about 0.1 to 1.0. These reactants are charged to a reaction vesselwhile maintaining the temperature below about 70° C. (160° F.), oftenabout 60° C. (140° F.). The order of addition is not critical, but it isimportant to take care during the addition of ammonia to formaldehyde(or formaldehyde to ammonia), due to the exothermic reaction. In fact,due to the strong exotherm, it may be preferred to charge theformaldehyde and the urea first, followed by the ammonia. This sequenceof addition allows one to take advantage of the endotherm caused by theaddition of urea to water to increase the rate of ammonia addition. Abase may be required to maintain an alkaline condition throughout thecook.

Once all the reactants are in the reaction vessel, the resultingsolution is heated at an alkaline pH to between about 60 and 105° C.(about 140 to about 220° F.), often about 85 to 95° C. (about 185 to205° F.), for 30 minutes to 3 hours, depending on mole ratio andtemperature, or until the reaction is complete. Once the reaction iscomplete, the solution is cooled to room temperature for storage. Theresulting solution is storage stable for several months at ambientconditions. The pH is between 5 and 11.

The yield is usually about 100%. The cyclic urea resins often contain atleast 20% triazone and substituted triazone compounds. The ratio ofcyclic ureas to di- and tri-substituted ureas and mono-substituted ureasvaries with the mole ratio of the reactants. For example, a cyclic urearesin having the mole ratio of 1.0:2.0:0.5 U:F:A resulted in a solutioncharacterized by C¹³-NMR and containing approximately 42.1% cyclicureas, 28.5% di/tri-substituted ureas, 24.5% mono-substituted ureas, and4.9% free urea. A cyclic urea resin having the mole ratio of 1.0:1.2:0.5U:F:A resulted in a solution characterized by C¹³-NMR and containingapproximately 25.7% cyclic ureas, 7.2% di/tri-substituted ureas, 31.9%mono-substituted ureas, and 35.2 free urea.

In addition, the cyclic urea-formaldehyde resin may be prepared by amethod such as described in U.S. Pat. No. 5,674,971. The cyclic urearesin is prepared by reacting urea and formaldehyde in at least a twostep and optionally a three-step process. In the first step, conductedunder alkaline reaction conditions, urea and formaldehyde are reacted inthe presence of ammonia, at an F/U mole ratio of between about 1.2:1 and1.8:1. The ammonia is supplied in an amount sufficient to yield anammonia/urea mole ratio of between about 0.05:1 and 1.2:1. The mixtureis reacted to form a cyclic triazone/triazine or cyclic urea resin.

Water soluble triazone compounds may also be prepared by reacting urea,formaldehyde and a primary amine as described in U.S. Pat. Nos.2,641,584 and 4,778,510. These patents also describe suitable primaryamines such as, but are not limited to, alkyl amines such as methylamine, ethyl amine, and propyl amine, lower hydroxyamines such asethanolamine cycloalkylmonoamines such as cyclopentylamine,ethylenediamine, hexamethylenediamine, and linear polyamines. Theprimary amine may be substituted or unsubstituted.

In the case of a cyclic urea-formaldehyde or a urea-formaldehyde resin,skilled practitioners recognize that the urea and formaldehyde reactantsare commercially available in many forms. Any form which is sufficientlyreactive and which does not introduce extraneous moieties deleterious tothe desired reactions and reaction products can be used in thepreparation of urea-formaldehyde resins useful in the invention. Forexample, commonly used forms of formaldehyde include paraform (solid,polymerized formaldehyde) and formalin solutions (aqueous solutions offormaldehyde, sometimes with methanol, in 37 percent, 44 percent, or 50percent formaldehyde concentrations). Formaldehyde also is available asa gas. Any of these forms is suitable for use in preparing aurea-formaldehyde resin. Typically, formalin solutions are used as theformaldehyde source. To prepare the resin of the present invention,formaldehyde may be substituted in whole or in part with any of thealdehydes described above (e.g., glyoxal).

Similarly, urea is commonly available in a variety of forms. Solid urea,such as prill, and urea solutions, typically aqueous solutions, arecommercially available. Any form of urea is suitable for use in thepractice of the invention. For example, many commercially preparedurea-formaldehyde solutions may be used, including combinedurea-formaldehyde products such as Urea-Formaldehyde Concentrate (e.g.,UFC 85) as disclosed in U.S. Pat. Nos. 5,362,842 and 5,389,716.

Also, urea-formaldehyde resins such as the types sold by Georgia PacificResins, Inc., Borden Chemical Co., and Neste Resins Corporation may beused. These resins are prepared as either low molecular weightcondensates or as adducts which, as described above, contain reactivemethylol groups that can undergo condensation to form resin polymers,often within the number average molecular weight ranges describedpreviously. The resins will generally contain small amounts of unreacted(i.e., free) urea and formaldehyde, as well as cyclic ureas,mono-methylolated urea, and di- and tri-methylolated ureas. The relativequantities of these species can vary, depending on the preparationconditions (e.g., the molar formaldehyde:urea ratio used). The balanceof these resins is generally water, ammonia, and formaldehyde. Variousadditives known in the art, including stabilizers, cure promoters,fillers, extenders, etc., may also be added to the resin.

The amine-aldehyde resins described above are highly selective forbinding with unwanted solid materials (e.g., sand or clay) and/or ionicspecies such as metallic cations to be separated in theseparation/purification processes of the present invention. Withoutbeing bound by theory, the amine-aldehyde resin of the presentinvention, in one embodiment, is generally cationic (i.e., carries moreoverall positive than negative charge) to attract most clay surfaces,which are generally anionic (i.e., carry more overall negative thanpositive charge). These differences in electronic characteristicsbetween the resin and clay can result in mutual attraction at multiplesites and even the potential sharing of electrons to form covalentbonds. The positive-negative charge interactions which cause clayparticles to become attracted to the resin is potentially explained byseveral theories, such as host-guest theory (including podands),hard-soft acid base theory, dipole-dipole interactions, Highest OccupiedMolecular Orbital-Lowest unoccupied Molecular Orbital (HOMO-LUMO)interactions, hydrogen bonding, Gibbs free energy of bonding, etc.

Silica, silicates, and/or polysiloxanes may be used in conjunction(e.g., added as a blending component) with the amine-aldehyde resin ofthe present invention to potentially improve its affinity for variousmaterials, especially siliceous materials including sand and clay,whether these materials be desired or unwanted in any particularapplication. Other agents that may be used to improve the performance ofresins in the separation processes of the present invention includepolysaccharides, polyvinyl alcohol, polyacrylamide, as well as knownflocculants (e.g., alginates). These agents can likewise be used withmodified urea-formaldehyde resins wherein, as described above, at leasta portion of the urea is replaced with ammonia or an amine as describedabove (e.g., primary alkylamines, alkanolamines, polyamines, etc.).Otherwise, such agents can also be used with resins which are modifiedwith anionic functional groups (e.g., sulfonate) or stabilized byetherification with an alcohol (e.g., methanol), as described below.

Silica in the form of an aqueous silica sol, for example, is availablefrom Akzo Nobel under the Registered Trademark “Bindzil” or from DuPontunder the Registered Trademark “Ludox”. Other grades of sol areavailable having various particle sizes of colloidal silica andcontaining various stabilizers. The sol can be stabilized by alkali, forexample sodium, potassium, or lithium hydroxide or quaternary ammoniumhydroxide, or by a water-soluble organic amine such as alkanolamine.

Silicates, such as alkali and alkaline earth metal silicates (e.g.,lithium silicate, sodium-lithium silicate, potassium silicate, magnesiumsilicate, and calcium silicate), as well as ammonium silicate or aquaternary ammonium silicate, may also be used in the preparation of theresin. Additionally, stabilized colloidal silica-silicate blends ormixtures, as described in U.S. Pat. No. 4,902,442, are applicable.

In the separation processes of the present invention, particularly goodperformance is obtained when the resin is prepared in a solution ordispersion, having a solids content from about 30% to about 90%, andtypically from about 45% to about 70%. Otherwise, “neat” forms of theresin, having little or no added solvent or dispersing agent (e.g.,water), may also be employed. In any event, usually at least about 90%by weight, and often at least about 95% by weight, of the amine andaldehyde components, used to form the resin, are reacted, in order toreduce the amounts of free (unreacted) amines and aldehydes. Thispractice more efficiently utilizes the amine and aldehyde components inthe production of the resin polymer, while minimizing any deleteriouseffects (e.g., vaporization into the environment) associated with thesecomponents in their free form. Overall, amine-aldehyde resins for use inseparation processes of the present invention generally contain fromabout 40% to about 100% resin solids or non-volatiles, and often 55% to75% non-volatiles. The non-volatiles content is measured by the weightloss upon heating a small (e.g., 1-5 gram), sample of the composition atabout 105° C. for about 3 hours. When an essentially “neat” form of theamine-aldehyde resin, having few or no volatile components, is employed,the pure resin may be added (e.g., as a viscous liquid, a gel, or asolid form, such as a powder), to the froth flotation slurry or liquiddispersion to be purified, such that an aqueous resin solution ordispersion is formed in situ. Neat forms of the amine-aldehyde resinsmay be obtained from solutions or dispersions of these resins usingconventional drying techniques, for example spray drying.

Aqueous solutions or dispersions of the resins of the present inventionwill generally be a clear liquid or a liquid having a white or yellowappearance. They will typically have a Brookfield viscosity from about75 to about 500 cps and a pH from about 6.5 to about 9.5. The freeformaldehyde content and free urea content of urea-formaldehyde resinsolutions are each typically below 5%, usually are each below 3%, andoften are each below 1%. A low content of formaldehyde is generallyachieved due to health concerns associated with exposure to formaldehydeemissions. If desired, conventional “formaldehyde scavengers” that areknown to react with free formaldehyde may be added to reduce the levelof formaldehyde in solution. Low amounts of free urea are alsodesirable, but for different reasons. Without being bound by theory,free urea is not believed to have the requisite molecular weight, (1) infroth flotation separations, to “blind” the gangue or desired (e.g.,clay) materials to their interaction with rising air bubbles, (2) in thepurification of liquid dispersions, to agglomerate a sufficiently largenumber of solid contaminant particles into flocs, or (3) in the removalof ionic species from aqueous solutions, to bind these species to amolecule of sufficient size for retention by filtration. In particular,it has been found that resin polymers having a number average molecularweight of greater than about 300 grams/mole exhibit the mass needed topromote efficient separations.

Froth Flotation

When used as depressants in froth flotation separations, resins of thepresent invention, due to their high selectivity, provide good resultsat economical addition levels. For example, the resins may be added inan amount from about 100 to about 1000 grams, and typically from about400 to about 600 grams, based on resin solution or dispersion weight,per metric ton of the material (e.g., clay-containing ore) that is to bepurified by froth flotation. In general, the optimal addition amount fora particular separation can be readily ascertained by those of skill inthe art and depends on number of factors, including the type and amountof impurities.

Resins of the present invention can be applied in the froth flotation ofa variety of materials (e.g., high molecular weight hydrocarbons such asbitumen) containing sand and/or clay, for which these resin depressantsare especially selective. Although clay is often considered an impurityin conventional metal or mineral ore beneficiation, it may also bepresent in relatively large quantities, as the main component to berecovered. Some clays, for example kaolin clay, are valuable minerals ina number of applications, such as mineral fillers in the manufacture ofpaper and rubber. Thus, one froth flotation process in which the resinof the present invention may be employed involves the separation of clayfrom a clay-containing ore. The impurities in such ores are generallymetals and their oxides, such as iron oxide and titanium dioxide, whichare preferentially floated via froth flotation. Other impurities ofclay-containing ores include coal. Impurities originally present in mostGeorgia kaolin, which are preferentially floated in the purificationmethod of the present invention, include iron-bearing titania andvarious minerals such as mica, ilmenite, or tourmaline, which aregenerally also iron-containing.

Thus, the clay, which selectively associates with the amine-aldehyderesin of the present invention, is separately recoverable from metals,metal oxides, and coal. In the purification of clay, it is oftenadvantageous to employ, in conjunction with the resin of the presentinvention as a depressant, an anionic collector such as oleic acid, aflocculent such as polyacrylamide, a clay dispersant such as a fattyacid or a rosin acid, and/or oils to control frothing. One approach,particularly in the refining of clay-containing ores, involves themodification of the resin with an anionic functional group, as describedin greater detail below.

The resin of the present invention is also advantageously employed inthe separation of bitumen from sand and/or clay that are co-extractedfrom natural oil sand deposits. Bitumen/sand mixtures that are removedfrom oil or tar sand deposits, often within several hundred feet of theearth's surface, are generally first mixed with warm or hot water tocreate an aqueous slurry of the oil sand, having a reduced viscositythat facilitates its transport (e.g., by pipeline) to processingfacilities. Steam and/or caustic solution may also be injected tocondition the slurry for froth flotation, as well as any number of otherpurification steps, described below. Aeration of the bitumen-containingslurry, comprising sand or clay, results in the selective flotation ofthe bitumen, which allows for its recovery as a purified product. Thisaeration may be effected by merely agitating the slurry to release airbubbles and/or introducing a source of air into the bottom of theseparation cell. The optimal amount of air needed to float the desiredbitumen, without entraining excessive solid contaminants, is readilydetermined by one of ordinary skill in the art.

Thus, the use of the resin depressant of the present inventionadvantageously promotes the retention of the sand and/or clay impuritiesin an aqueous fraction, which is removed from the bottom section of thefroth flotation vessel. This bottoms fraction is enriched (i.e., has ahigher concentration of) the sand and/or clay impurities, relative tothe initial bitumen slurry. The overall purification of bitumen may relyon two or more stages of flotation separation. For example, the middlesection of a primary flotation separation vessel may contain asignificant amount of bitumen that can ultimately be recovered in asecondary flotation of this “middlings” fraction.

Generally, in any froth flotation process according to the presentinvention, at least 70% of the value material (e.g., bitumen or kaolinclay) is recovered from the raw material (e.g., the clay-containingore), with a purity of at least 85% by weight. Also, conventional knowncollectors may be used in conjunction with resins of the presentinvention, when used as depressants. These collectors include, forexample, fatty acids (e.g., oleic acid, sodium oleate, hydrocarbonoils), amines (e.g., dodecylamine, octadecylamine, α-aminoarylphosphonicacid, and sodium sarcosinate), and xanthanate. Likewise, conventionaldepressants known in the art can also be combined with the resindepressants. Conventional depressants include guar gum and otherhydrocolloidal polysaccharides, sodium hexametaphosphate, etc.Conventional frothing agents that aid collection, (e.g.,methylisobutylcarbinol, pine oil, and polypropylene oxides) may also beused, in accordance with normal flotation practice, in conjunction withthe resin depressants of the present invention.

In froth flotation separations, the pH of the slurry to which the resinsof the present invention, when used as depressants, are added will varyaccording to the particular material to be processed, as is appreciatedby those skilled in the art. Commonly, the pH values range from neutral(pH 7) to strongly alkaline (e.g., pH 12). It is recognized that in someflotation systems, high pH values (e.g., from about 8 to about 12.5)give best results.

Typically in froth flotation for the beneficiation of solid materials,the raw ore to be subjected to beneficiation is usually first ground tothe “liberation mesh” size. The solid material may be ground to produce,for example, one-eighth inch average diameter particles prior toincorporation of the material into a brine solution to yield an aqueousslurry. After crushing and slurrying the material, the slurry may beagitated or stirred in a “scrubbing” process that breaks down some ofthe solids into very fine particles that remain in the brine as a muddysuspension. Some of these fines may be washed off the ore particlesprior to froth flotation. Also, as is known in the art, any conventionalpreconditioning steps including further crushing/screening, cycloning,and/or hydro separation steps, may be employed, respectively, to furtherreduce/classify raw material particle size and/or recover smaller solidparticles, prior to froth flotation.

Before or during froth flotation, the resin of the present invention, tobe used as a depressant, is added to the aqueous slurry, usually in amanner such that the depressant is readily dispersed throughout. Asstated above, conventional collectors may also be used to aid in theflotation of certain materials. In the froth flotation process, theslurry, typically having a solids content from about 10 to about 50% byweight, is transferred to one or more froth flotation cells. Air isforced through the bottoms of these cells and a relatively hydrophobicfraction of the material, having a selective affinity for the risingbubbles, floats to the surface (i.e., the froth), where it is skimmedoff and recovered. A bottoms product that is hydrophilic relative to thefroth concentrate, may also be recovered. The process may be accompaniedby agitation. Commercially salable products can be prepared from theseparate fractions recovered in this manner, often after furtherconventional steps, including separation (e.g., by centrifuge), drying(e.g., in a gas fired kiln), size classification (e.g., screening), andrefining (e.g., crystallization), are employed.

The froth flotation of the present invention may, though not always,involve flotation in “rougher cells” followed by one or more “cleanings”of the rougher concentrate. Two or more flotation steps may also beemployed to first recover a bulk material comprising more than onecomponent, followed by a selective flotation to separate thesecomponents. Amine-aldehyde resins of the present invention, when used asdepressants, can be used to advantage in any of these steps to improvethe selective recovery of desired materials via froth flotation. Whenmultiple stages of froth flotation are used, the resins may be addedusing a single addition prior to multiple flotations or they may beadded separately at each flotation stage.

Other Separations

Because of their affinity for solid contaminants in liquid suspensionsor slurries, the amine-aldehyde resins of the present invention areapplicable in a wide variety of separations, and especially thoseinvolving the removal of siliceous contaminants such as sand and/or clayfrom aqueous liquid suspensions or slurries of these contaminants. Suchaqueous suspensions or slurries may therefore be treated withamine-aldehyde resins of the present invention, allowing for theseparation of at least a portion of the contaminants, in acontaminant-rich fraction, from a purified liquid. A “contaminant-rich”fraction refers to a part of the liquid suspension or slurry that isenriched in solid contaminants (i.e., contains a higher percentage ofsolid contaminants than originally present in the liquid suspension orslurry). Conversely, the purified liquid has a lower percentage of solidcontaminants than originally present in the liquid suspension or slurry.

The separation processes described herein are applicable to“suspensions” as well as to “slurries” of solid particles. These termsare sometimes defined equivalently and sometimes are distinguished basedon the need for the input of at least some agitation or energy tomaintain homogeneity in the case of a “slurry.” Because the methods ofthe present invention, described herein, are applicable broadly to theseparation of solid particles from aqueous media, the term “suspension”is interchangeable with “slurry” (and vice versa) in the presentspecification and appended claims.

The treatment step may involve adding a sufficient amount of theamine-aldehyde resin to electronically interact with and eithercoagulate or flocculate the solid contaminants into larger agglomerates.The necessary amount can be readily determined depending on a number ofvariables (e.g., the type and concentration of contaminant), as isreadily appreciated by those having skill in the art. In otherembodiments, the treatment may involve contacting the liquid suspensioncontinuously with a fixed bed of the resin, in solid form.

During or after the treatment of a liquid suspension with theamine-aldehyde resin, the coagulated or flocculated solid contaminant(which may now be, for example, in the form of larger, agglomeratedparticles or flocs) is removed. Removal may be effected by flotation(with or without the use of rising air bubbles as described previouslywith respect to froth flotation) or sedimentation. The optimal approachfor removal will depend on the relative density of the flocs and otherfactors. Increasing the quantity of resin that is used to treat thesuspension can in some cases increase the tendency of the flocs to floatrather than settle. Filtration or straining may also be an effectivemeans of removing the agglomerated flocs of solid particulates,regardless of whether they reside in a surface layer or in a sediment.

Examples of liquid suspensions that may be purified according to thepresent invention include oil and gas well drilling fluids, whichaccumulate solid particles of rock (or drill cuttings) in the normalcourse of their use. These drilling fluids (often referred to as“drilling muds”) are important in the drilling process for severalreasons, including transporting these drill cuttings from the drillingarea to the surface, where their removal allows the drilling mud to berecirculated. The addition of amine-aldehyde resins of the presentinvention to oil well drilling fluids, and especially water-based (i.e.,aqueous) drilling fluids, effectively coagulates or flocculates solidparticle contaminants into larger clumps into larger clumps (or flocs),thereby facilitating their separation by settling or flotation. Theresins of the present invention may be used in conjunction with knownflocculants for this application such as polyacrylamides orhydrocolloidal polysaccharides. Often, in the case of suspensions ofwater-based oil or gas well drilling fluids, the separation of the solidcontaminants is sufficient to provide a purified drilling fluid forreuse in drilling operations.

Other aqueous suspensions of practical interest include theclay-containing aqueous suspensions or brines, which accompany orerefinement processes, including those described above. The production ofpurified phosphate from mined calcium phosphate rock, for example,generally relies on multiple separations of solid particulates fromaqueous media, whereby such separations can be improved using the resinof the present invention. In the overall process, calcium phosphate ismined from deposits at an average depth of about 25 feet below groundlevel. The phosphate rock is initially recovered in a matrix containingsand and clay impurities. The matrix is first mixed with water to form aslurry, which, typically after mechanical agitation, is screened toretain phosphate pebbles and to allow fine clay particles to passthrough as a clay slurry effluent with large amounts of water.

These clay-containing effluents generally have high flow rates andtypically carry less than 10% solids by weight and more often containonly from about 1% to about 5% solids by weight. The dewatering (e.g.,by settling or filtration) of this waste clay, which allows for recycleof the water, poses a significant challenge for reclamation. The timerequired to dewater the clay, however, can be decreased throughtreatment of the clay slurry effluent, obtained in the production ofphosphate, with the amine-aldehyde resin of the present invention.Reduction in the clay settling time allows for efficient re-use of thepurified water, obtained from clay dewatering, in the phosphateproduction operation. In one embodiment of the purification method,wherein the liquid suspension is a clay-containing effluent slurry froma phosphate production facility, the purified liquid contains less thanabout 1% solids by weight after a settling or dewatering time of lessthan about 1 month.

In addition to the phosphate pebbles that are retained by screening andthe clay slurry effluent described above, a mixture of sand and finerparticles of phosphate is also obtained in the initial processing of themined phosphate matrix. The sand and phosphate in this stream areseparated by froth flotation which, as described earlier, can beimproved using the amine-aldehyde resin of the present invention as adepressant for the sand.

In the area of slurry dewatering, another specific application of theresin is in the filtration of coal from water-containing slurries. Thedewatering of coal is important commercially, since the BTU value andhence the quality of the coal decreases with increasing water content.In one embodiment of the invention, therefore, the amine-aldehyde resinis used to treat an aqueous coal-containing suspension or slurry priorto dewatering the coal by filtration.

Another significant application of the amine-aldehyde resin of thepresent invention is in the area of sewage treatment, which refers tovarious processes that are undertaken to remove contaminants fromindustrial and municipal waste water. Such processes thereby purifysewage to provide both purified water that is suitable for disposal intothe environment (e.g., rivers, streams, and oceans) as well as a sludge.Sewage refers to any type of water-containing wastes which are normallycollected in sewer systems and conveyed to treatment facilities. Sewagetherefore includes municipal wastes from toilets (sometimes referred toas “foul waste”) and basins, baths, showers, and kitchens (sometimesreferred to as “sullage water”). Sewage also includes industrial andcommercial waste water, (sometimes referred to as “trade waste”), aswell as stormwater runoff from hard-standing areas such as roofs andstreets.

The conventional treatment of sewage often involves preliminary,primary, and secondary treatment steps. Preliminary treatment refers tothe filtration or screening of large solids such as wood, paper, rags,etc., as well as coarse sand and grit, which would normally damagepumps. The subsequent primary treatment is then employed to separatemost of the remaining solids by settling in large tanks, where asolids-rich sludge is recovered from the bottom of these tanks andtreated further. A purified water is also recovered and normallysubjected to secondary treatment by biological processes.

Thus, in one embodiment of the present invention, the settling orsedimentation of sewage water may comprise treating the sewage with theamine-aldehyde resin of the present invention. This treatment may beused to improve the settling operation (either batch or continuous), forexample, by decreasing the residence time required to effect a givenseparation (e.g., based on the purity of the purified water and/or thepercent recovery of solids in the sludge). Otherwise, the improvementmay be manifested in the generation of a higher purity of the purifiedwater and/or a higher recovery of solids in the sludge, for a givensettling time.

After treatment of sewage with the amine-aldehyde resin of the presentinvention and removing a purified water stream by sedimentation, it isalso possible for the amine-aldehyde resin to be subsequently used for,or introduced into, secondary treatment processes to further purify thewater. Secondary treatment normally relies on the action of naturallyoccurring microorganisms to break down organic material. In particular,aerobic biological processes substantially degrade the biologicalcontent of the purified water recovered from primary treatment. Themicroorganisms (e.g., bacteria and protozoa) consume biodegradablesoluble organic contaminants (e.g., sugars, fats, and other organicmolecules) and bind much of the less soluble fractions into flocs,thereby further facilitating the removal of organic material.

Secondary treatment relies on “feeding” the aerobic microorganismsoxygen and other nutrients which allow them to survive and consumeorganic contaminants. Advantageously, the amine-aldehyde resin of thepresent invention, which contains nitrogen, can serve as a “food” sourcefor microorganisms involved in secondary treatment, as well aspotentially an additional flocculant for organic materials. In oneembodiment of the invention, therefore, the sewage purification methodfurther comprises, after removing purified water (in the primarytreatment step) by sedimentation, further treating the purified water inthe presence of microorganisms and the amine-aldehyde resin, andoptionally with an additional amount of amine-aldehyde resin, to reducethe biochemical oxygen demand (BOD) of the purified water. As isunderstood in the art, the BOD is an important measure of water qualityand represents the oxygen needed, in mg/l (or ppm by weight) bymicroorganisms to oxidize organic impurities over 5 days. The BOD of thepurified water after treatment with microorganisms and theamine-aldehyde resin, is generally less than 10 ppm, typically less than5 ppm, and often less than 1 ppm.

The amine-aldehyde resin of the present invention may also be applied tothe purification of pulp and paper mill effluents. These aqueous wastestreams normally contain solid contaminants in the form of cellulosicmaterials (e.g., waste paper; bark or other wood elements, such as woodflakes, wood strands, wood fibers, or wood particles; or plant fiberssuch as wheat straw fibers, rice fibers, switchgrass fibers, soybeanstalk fibers, bagasse fibers, or cornstalk fibers; and mixtures of thesecontaminants). In accordance with the method of the present invention,the effluent stream comprising a cellulosic solid contaminant is treatedwith the amine-aldehyde resin of the present invention, such thatpurified water may be removed via sedimentation, flotation, orfiltration.

In the separation of bitumen from sand and/or clay impurities asdescribed previously, various separation steps may be employed eitherbefore or after froth flotation of the bitumen-containing slurry. Thesesteps can include screening, filtration, and sedimentation, any of whichmay benefit from treatment of the oil sand slurry with theamine-aldehyde resin of the present invention, followed by removal of aportion of the sand and/or clay contaminants in a contaminant-richfraction (e.g., a bottoms fraction) or by removal of a purified bitumenfraction. As described above with respect to phosphate ore processingwater effluents, which generally contain solid clay particles, thetreating step can comprise flocculating these contaminants to facilitatetheir removal (e.g., by filtration). Waste water effluents from bitumenprocessing facilities will likewise contain sand and/or clay impuritiesand therefore benefit from treatment with the amine-aldehyde resin ofthe present invention to dewater them and/or remove at least a portionof these solid impurities in a contaminant-rich faction. A particularprocess stream of interest that is generated during bitumen extractionis known as the “mature fine tails,” which is an aqueous suspension offine solid particulates that can benefit from dewatering. Often, in thecase of sand and/or clay containing suspensions from a bitumenproduction facility, separation of the solid contaminants is sufficientto allow the recovery or removal of a purified liquid or water streamthat can be recycled to the bitumen process.

The treatment of various intermediate streams and effluents in bitumenproduction processes with the resin of the present invention is notlimited only to those processes that rely at least partly on frothflotation of an aqueous bitumen-containing slurry. As is readilyappreciated by those of skill in the art, other techniques (e.g.,centrifugation via the “Syncrude Process”) for bitumen purification willgenerate aqueous intermediate and byproduct streams from which solidcontaminant removal is desirable.

The amine-aldehyde resins of the present invention can be employed inthe removal of suspended solid particulates, such as sand and clay, inthe purification of water, and particularly for the purpose of renderingit potable. Moreover, resins of the present invention have theadditional ability to complex metallic cations (e.g., lead and mercurycations) allowing these unwanted contaminants to be removed inconjunction with solid particulates. Therefore, resins of the presentinvention can be used to effectively treat impure water having bothsolid particulate contaminants as well as metallic cation contaminants.Without being bound by theory, it is believed that electronegativemoieties, such as the carbonyl oxygen atom on the urea-formaldehyderesin polymer backbone, complex with undesired cations to facilitatetheir removal. Generally, this complexation occurs at a pH of the waterthat is greater than about 5 and typically in the range from about 7 toabout 9.

Another possible mechanism for the removal of metallic cations is basedon their association with negatively charged solid particulates.Flocculation and removal of these particulates will therefore alsocause, at least to some extent, the removal of metallic cations.Regardless of the mechanism, in one embodiment, the treatment andremoval of both of these contaminants can be carried out according tothe present invention to yield potable water.

The removal of metallic cations may represent the predominant or eventhe sole means of water purification that is effected by theamine-aldehyde resin, for example when the water to be purified containslittle or no solid particulates. Solid forms of the resin may be used toremove cations in a continuous process whereby the impure watercontaining metallic cations is continuously passed through a fixed bedof the resin. Alternatively, soluble forms of the resin, generallyhaving a lower molecular weight, may be added to the impure water inorder to treat it. The complexed cations in this case can be removed,for example, by ultrafiltration through a porous membrane (e.g.,polysulfone) having a molecular weight cutoff that is less than themolecular weight of the resin. The water purification methods describedherein may also be used in conjunction with known methods includingreverse osmosis, UV irradiation, etc.

To increase the effectiveness of resins of the present invention incomplexing with metallic cations, it may be desirable to modify thisamine-aldehyde resin with one or more anionic functional groups. Suchmodifications are known in the art and can involve the reaction of theresin to incorporate the desired functional group (e.g., by sulfonationwith sodium metabisulfite). Alternatively, the modification is achievedduring preparation of the resin (e.g., during condensation) byincorporating an anionic co-monomer, such as sodium acrylate, into theamine-aldehyde resin. Representative functionalities with which theresin, including a urea-formaldehyde resin, may be modified include theanionic functional groups bisulfite, acrylate, acetate, carbonate,azide, amide, etc. Procedures for modifying the resin with additionalfunctionalities are known to those having skill in the art. Theincorporation of anionic functional groups into the resin is also oftenemployed in separations involving the purification of slurriescontaining solid clay particles (e.g., by froth flotation, flocculation,etc.), including the purification of kaolin clay ore. Without beingbound by theory, sulfonation of the resin or the incorporation of otheranionic functional groups can also increase hydrogen bonding between theresin and the surrounding aqueous phase to inhibit condensation of theresin or otherwise improve its stability.

As described above, therefore, the present invention, in one embodiment,is a method for purifying water containing a metallic cation by treatingthe water with an amine-aldehyde resin as described herein and which maybe modified with an anionic group. Removal of at least a portion of themetallic cations may be effected by retaining them on a fixed bed of theresin or otherwise by filtering them out. In the latter case, removal byfiltration such as membrane filtration is made possible by theassociation of the metallic cations either directly with theamine-aldehyde resin or indirectly with the resin via solidparticulates, for which the resin has affinity. In the case of indirectassociation, as described earlier, flocculation of the solidparticulates will also necessarily agglomerate at least a portion of themetallic cations, which may therefore be removed by flotation orsedimentation of these particulates.

The amine-aldehyde resin of the present invention is thereforeadvantageously used to treat water for the removal of metallic cationssuch as arsenic, lead, cadmium, copper, and mercury that are known topose health risks when ingested. These cations thus include As⁺⁵, Pb⁺²,Cd⁺², Cu⁺², Hg⁺², and mixtures thereof. Generally, a degree of removalis effected such that the purified water, after treatment, isessentially free of one or more of the above metallic cations. By“essentially free” is meant that the concentration(s) of one or moremetallic cation(s) of interest is/are reduced to concentration(s) at orbelow those considered safe (e.g., by a regulatory agency such as theU.S. Environmental Protection Agency). Therefore, in variousembodiments, the purified water will contain at most about 10 ppb ofAs⁺⁵, at most about 15 ppb of Pb⁺², at most about 5 ppb of Cd⁺², at mostabout 1.3 ppm of Cu⁺², and/or at most about 2 ppb of Hg⁺². That is,generally at least one, typically at least two, and often all, of theabove-mentioned cations are at or below these threshold concentrationlevels in the purified water.

In any of the applications described herein, it is possible to stabilizethe amine-aldehyde resin of the present invention by reaction with analcohol (i.e., etherification). Without being bound by theory, it isbelieved that etherification of pendant alkylol functionalities caninhibit further condensation of the amine-aldehyde resin (e.g.,condensation of the urea-formaldehyde resin with itself). This canultimately hinder or prevent the precipitation of the resin during longterm storage, such that, relative to their corresponding non-etherifiedresins, the etherified resins can have increased molecular weightwithout an accompanying loss in stability.

Etherification thus involves reacting the amine-aldehyde adducts orcondensates, or even the resins, prepared as described above, with analcohol. In one embodiment, a urea-formaldehyde resin is etherified withan alcohol having from 1 to 8 carbon atoms. Representative alcohols foruse in the etherification include methanol (e.g., to effectmethylation), ethanol, n-propanol, isopropanol, n-butanol, andisobutanol. In exemplary preparations of etherified resins, theamine-aldehyde adduct or condensate reaction product is heated to atemperature from about 70° C. to about 120° C. in the presence of analcohol until the etherification is complete. An acid such as sulfuricacid, phosphoric acid, formic acid, acetic acid, nitric acid, alum, ironchloride, and other acids may be added before or during the reactionwith alcohol. Often, sulfuric acid or phosphoric acid is employed.

All references cited in this specification, including withoutlimitation, all U.S., international, and foreign patents and patentapplications, as well as all abstracts and papers (e.g., journalarticles, periodicals, etc.), are hereby incorporated by reference intothis specification in their entireties. The discussion of the referencesherein is intended merely to summarize the assertions made by theirauthors and no admission is made that any reference constitutes priorart. Applicants reserve the right to challenge the accuracy andpertinence of the cited references. In view of the above, it will beseen that several advantages of the invention are achieved and otheradvantageous results obtained.

As various changes could be made in the above methods and compositionswithout departing from the scope of the invention, it is intended thatall matter contained in this application, including all theoreticalmechanisms and/or modes of interaction described above, shall beinterpreted as illustrative only and not limiting in any way the scopeof the appended claims.

The following examples are set forth as representative of the presentinvention. These examples are not to be construed as limiting the scopeof the invention as these and other equivalent embodiments will beapparent in view of the present disclosure and appended claims.

EXAMPLE 1

Various urea-formaldehyde resins were prepared as low molecular weightcondensate resins, initially under alkaline conditions to formmethylolated urea adducts, and then under acidic conditions to form thecondensate. The condensation reaction was stopped by raising the pH ofthe condensation reaction mixture. Other preparation conditions were asdescribed above. These resins are identified in Table 1 below withrespect to their molecular weight (Mol. Wt.) in grams/mole and theirapproximate normalized weight percentages of free urea, cyclic ureaspecies (cyclic urea), mono-methylolated urea (Mono), and combineddi-/tri-methylolated urea (Di/Tri). In each case, the resins were in asolution having a resin solids content of 45-70%, a viscosity of 500 cpsor less, and a free formaldehyde content of less than 5% by weight.

TABLE 1 Urea-Formaldehyde Resins Free ID Mol. Wt.^(a) Urea Cyclic UreaMono Di/Tri Resin A 406 8 39 30 23 Resin B* 997 5 50 22 23 Resin C andC′** 500 6 46 25 23 Resin D and D′*** 131 43  21 30  6 Resin E 578 0 1810 72 Resin F 1158  1 44 11 44 Resin G 619 0 26  3 71 *Resin B is a verystable urea-formaldehyde resin, having a high cyclic urea content. Thisresin is described in U.S. Pat. No. 6,114,491. **Resin C′ was formed byadding 2% by weight of diethylenetriamine and 2% by weight dicyandiamideto the mixture of urea and formaldehyde during resin preparation.***Resin D′ was formed by adding 0.75% by weight cyclic phosphate esterto the mixture of urea and formaldehyde during resin preparation. Theresin was a low molecular weight formulation with a high content of freeurea, essentially no free formaldehyde, and a high content ofnon-volatiles (about 70% solids). ^(a)Number average molecular weightdetermined using gel permeation chromatography (GPC) with appropriatelysized PLgel ™ columns (Polymer Laboratories, Inc., Amherst, MA, USA),0.5% glacial acetic acid/tetrahydrofuran mobile phase at 1500 psi, andpolystyrene, phenol, and bisphenol-A calibration standards.

EXAMPLE 2

Samples of urea-formaldehyde (UF) resins similar to those described inExample 1 were tested for their ability to settle graphite andbentonite, suspended in aqueous media. In four separate experiments, 4.4gram samples of particulate graphite (two experiments) and particulatebentonite (two experiments) were suspended in 220 grams of water in ajar, and the jars were in each case shaken vigorously for two minutes tosuspend the solid particles. However, 22 grams of UF resin were added toone of the jars containing the graphite and also to one of the jarscontaining bentonite prior to shaking. The four jars were left to standfor 24 hours and observed to evaluate the effect of the added UF resinon the solid-liquid separation via settling. The four jars werephotographed and are shown in FIG. 1.

As is apparent from FIG. 1, in the leftmost jar, to which UF resin wasadded, the graphite was settled on the bottom of the jar. No graphitewas visible at the air-water interface or on the jar surface. The UFresin used in this case also settled with the graphite. In contrast, thesecond jar from the left, to which no resin was added, had a significantamount of the graphite clinging to its surface. Much of the graphitealso remained at the air-water interface. The use of UF resin,therefore, greatly facilitated the separation of graphite from water viasettling.

Likewise, the bentonite was settled on the bottom of the third jar fromthe left, to which UF resin was added. The opaqueness of the liquidphase resulted from the use, in this case, of a water-dispersible UFresin. In contrast, the rightmost jar, to which no resin was added, hada significant amount of solid bentonite clinging to its surface andremaining at the air-water interface. Again, the use of UF resinsignificantly improved the separation of bentonite via settling.

EXAMPLE 3

A urea-formaldehyde (UF) resin similar to those described in Example 1,was tested for its ability to reduce the dewatering time, by filtration,of various solid contaminants (i.e., montmorillonite, bentonite, andgraphite) suspended in aqueous slurries. In each experiment, a 25 gramsample of solid contaminant was uniformly slurried with 100 grams of0.01 molar KNO₃. The pH of the slurry was measured. The slurry was thensubjected to vacuum filtration using a standard 12.7 cm diameter Buchnerfunnel apparatus and 11.0 cm diameter Whatman qualitative #1 filterpaper. Except for the first experiment using montmorillonte, thedewatering time in each case was the time required to recover 100 ml offiltrate through the filter paper. In the case of montmorillonitedewatering, the solid used was so fine that an excess of 5 minutes wouldhave been required to remove 100 ml of filtrate. Therefore, the relativedewatering time was based on the amount of filtrate removed in 5minutes.

For each solid contaminant tested, a control experiment as run, followedby an identical experiment, differing only in (1) the addition of 0.5-1grams of silane modified UF resin to the slurry and (2) mixing of theslurry for one additional minute, after a uniform slurry was obtainedupon stirring. Results are shown below in Table 2.

TABLE 2 Dewatering Time for Aqueous Slurries (25 grams Solid Contaminantin 100 grams 0.01 M KNO₃) Control + 0.5–1 grams Solid Control UF ResinMontmorillonite 11.8 grams* 14.2 grams* (slurry pH) (8.5) (8.6)Bentonite 138 seconds** 37 seconds*** (slurry pH) (8.0) (8.3) Graphite9.4^(†) 6.1^(††) (slurry pH) (4.4) (4.3) *amount of water removed over 5minutes **average of two experiments (139 seconds / 137 seconds)***average of two experiments (35 seconds / 38 seconds) ^(†)average oftwo experiments (9.3 seconds / 9.5 seconds) ^(††)average of twoexperiments (5.9 seconds / 6.2 seconds)

The above results demonstrate the ability of UF resins, even when usedin small quantities, to significantly decrease the dewatering time for anumber of solid particles.

What is claimed is:
 1. A method for purifying an aqueous liquidsuspension, comprising: treating a liquid suspension comprising claywith a urea-formaldehyde resin having a formaldehyde to urea molar ratioof about 1.5:1 to about 4:1, wherein an alkaline reaction condition ismaintained throughout the synthesis of the urea-formaldehyde resin; andremoving, either after or during the treating step, a purified liquid orat least a portion of the clay by sedimentation or floatation.
 2. Themethod of claim 1, wherein treating the liquid suspension comprisesflocculating the clay.
 3. The method of claim 1, wherein at least aportion of the clay is removed by sedimentation.
 4. The method of claim1, wherein the liquid suspension is from a phosphate productionfacility.
 5. The method of claim 4, wherein the purified water isremoved for reuse in phosphate production.
 6. The method of claim 1,wherein the urea-formaldehyde resin is modified with one or more anionicfunctional groups.
 7. The method of claim 1, wherein theurea-formaldehyde resin is stabilized by reacting with an alcoholcomprising ethanol, n-propanol, isopropanol, n-butanol, or isobutanol.8. The method of claim 1, wherein the urea-formaldehyde resin has aconcentration of free formaldehyde of less than 1%, based on the totalweight of the urea-formaldehyde resin.
 9. The method of claim 1, whereinthe urea-formaldehyde resin is formed by reacting a monomer mixtureconsisting essentially of urea and formaldehyde.
 10. The method of claim1, wherein the urea-formaldehyde resin has a number average molecularweight (Mn) of about 400 grams per mole to about 1,200 grams per mole.11. The method of claim 1, wherein the urea-formaldehyde resin has aconcentration of free formaldehyde of less than 1%, based on the totalweight of the urea-formaldehyde resin, the urea-formaldehyde resin has anumber average molecular weight (Mn) of about 400 grams per mole toabout 1,200 grams per mole, and the urea-formaldehyde resin isstabilized by reacting with an alcohol comprising ethanol, n-propanol,isopropanol, n-butanol, or isobutanol.
 12. A method for purifying anaqueous liquid suspension, comprising: treating a liquid suspensioncomprising a solid contaminant with a generally cationicurea-formaldehyde resin having a formaldehyde to urea molar ratio ofabout 1.5:1 to about 4:1, wherein an alkaline reaction condition ismaintained throughout the synthesis of the urea-formaldehyde resin; andremoving, either after or during the treating step, a purified liquid orat least a portion of the solid contaminant by sedimentation orfloatation.
 13. The method of claim 12, wherein treating the liquidsuspension comprises flocculating the solid contaminant.
 14. The methodof claim 12, wherein at least a portion of the solid contaminant isremoved by sedimentation.
 15. The method of claim 12, wherein the liquidsuspension is from a phosphate production facility.
 16. The method ofclaim 15, wherein the purified water is removed for reuse in phosphateproduction.
 17. The method of claim 12, wherein the solid contaminantcomprises sand, clay, or a combination thereof.
 18. The method of claim17, wherein the liquid suspension is a clay-containing effluent slurryfrom a phosphate production facility.
 19. The method of claim 12,wherein the urea-formaldehyde resin is etherified with an alcoholselected from the group consisting of: ethanol, n-propanol, isopropanol,n-butanol, and isobutanol.
 20. The method of claim 12, wherein the atleast a portion of the solid contaminant is removed by floatation. 21.The method of claim 20, wherein the floatation comprises frothfloatation.
 22. The method of claim 12, wherein the urea-formaldehyderesin has a number average molecular weight ranging from about 400 gramsper mole to about 1,200 grams per mole.
 23. The method of claim 12,wherein the urea-formaldehyde resin is formed by reacting a monomermixture consisting essentially of urea and formaldehyde.
 24. The methodof claim 12, wherein the urea-formaldehyde resin has a concentration offree formaldehyde of less than 1%, based on the total weight of theurea-formaldehyde resin.
 25. The method of claim 12, wherein theurea-formaldehyde resin has a concentration of free formaldehyde of lessthan 1%, based on the total weight of the urea-formaldehyde resin, theurea-formaldehyde resin has a number average molecular weight (Mn) ofabout 400 grams per mole to about 1,200 grams per mole, and theurea-formaldehyde resin is stabilized by reacting with an alcoholcomprising ethanol, n-propanol, isopropanol, n-butanol, or isobutanol.26. The method of claim 12, wherein the urea-formaldehyde resin has aformaldehyde to urea molar ratio of about 2:1 to about 3:1, theurea-formaldehyde resin has a concentration of free formaldehyde of lessthan 1%, based on the total weight of the urea-formaldehyde resin, theurea-formaldehyde resin is stabilized by reacting with an alcoholcomprising ethanol, n-propanol, isopropanol, n-butanol, or isobutanol,and the urea-formaldehyde resin is formed by reacting a monomer mixtureconsisting essentially of urea and formaldehyde or a monomer mixtureconsisting essentially of urea, formaldehyde, and ammonia.